One way of improving polymer properties is by adding a natural or synthetic clay material to polymers to form composite materials. However, incorporating clays into polymers may not provide a desirable improvement in the physical properties, particularly mechanical and optical properties of the polymer may be adversely affected.
Nanocomposite compositions containing finely dispersed natural or synthetic clay with at least partially intercalated and/or exfoliated layers and mixtures of ethylenically unsaturated monomers and/or polymers therefrom have therefore attracted much interest in the last years. These materials combine the desired effects of dispersed clay by avoiding the negative influence on, for example, the mechanical or optical properties.
Such compositions, methods for making them and their use in polymers and coatings are for example described in WO 02/24759. Polymerization processes are described using montmorillonite clay, acrylate monomers and for example ammonium persulfate as radical initiator. This conventional polymerization process leads to polymers with broad molecular weight distributions and a high polydispersity index (PD).
Y. Sogah et al., J. Am. Chem. Soc. 1999, 121, 1615-1616 describe the synthesis of dispersed nanocomposite compositions by in situ living free radical polymerization of styrene using a silicate-anchored initiator. The nitroxyl compound used is a 2,2,6,6 tetramethylpiperidine alkoxyamine. Although Sogah et al. have shown the principal possibility of preparing nanocomposite compositions by controlled free radical polymerization, they have been limited to styrene, since the known initiators/regulators are not efficient enough to polymerize acrylates or methacrylates with reasonable conversion rates at acceptable temperatures.